Our long-term goal is to define the electrophysiological, morphological and biochemical correlates of synapes formation. Most experiments are performed with cultures of cells dissociated from embryonic chick spinal cords ciliary ganglia, sensory ganglia and muscle. In nerve-muscle co-cultures, patch-clamp microelectrodes will be used to describe parameters of acetylcholine (ACh) release from growth cones and newly formed synapes, and also to monitor the accumulation of ACh receptors and acetylcholinesterase (AChE) in the postsynaptic complex. Reverse-phase HPLC and other chromatographic techniques will be used to purify factors from neural tissue that induce the synthesis of ACh receptors and AChE. Antibodies raised against purified material will be used to localize the activity and to study its role in normal development. the influence of competing neurons and of impulse activity on the stability of synapses will be studied in a new microculture system. In spinal cord-sensory neuron co-cultures, the specificity and function of synapses formed on identified motoneurons (labeled in vivo with a fluorescent probe via retrograde axonal transport) will be tested. Patch-clamp techniques will be used to assay transmitter condidates, to map the distribution of chemoreceptors, and to analyze the inonic basis of presynaptic and postsynaptic inhibition. Information about the function, stability and specificity of newly formed synapses has import for developmental neurological defects, for neural mechanisms that underlie learning and memory, and for mechanisms of degeneration and regeneration in the mature brain.